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for this method is that of Scheibler and Dietrich, of which the essential
features are shown in Fig. 6. It consists of a wide-necked bottle with a
perforated stopper by which it is connected with a vertical tube c. The latter
is joined at the top through a 3-way cock—which can establish communi-
cation also with the outside air—with a graduated cylinder a, which is
connected by a rubber tube at the bottom with a wide tube b capable
of being raised or lowered at will. All joints must, of course, be quite

From 0-5 to 0-6 gram of the substance is placed in the bottle, together
with a small tube containing hydrochloric acid, arranged so that, when
the bottle is inclined, the acid falls on the sub-
stance. The tube a is filled with water (coloured
red with litmus and a little boric acid, to admit
of more easy reading) to the top of the gradua-
tions and the pressures inside and outside of it
being equalised, the carbon dioxide is liberated by
bringing the acid into contact with the substance
in the bottle. The pressures are then equalised
and the volume of the gas read off, the result
being corrected in the usual way.

A more convenient procedure consists in
weighing such a quantity of substance—depend-
ing on the temperature and pressure and deter-
mined by means of special tables x—that the
volume of gas read off gives directly the percent-
age of calcium carbonate in the substance.

Of the other forms of apparatus, that of
Lunge and Rittener may be mentioned as allow-
ing of increased accuracy.

5.  Organic and Bituminous Substances.—
These are deduced by subtracting, from the loss
on ignition, both the   combined  water  and the
carbon dioxide, obtainable as under 3 and 4.

6.   Silica.—(a)   Total   silica.     The  calcined
substance   (that  remaining   after the determina-
tion of the loss on ignition) is evaporated to dry-
ness with a little water and hydrochloric acid in
a   porcelain   dish,   the   insoluble   residue   being

stirred from time to time with a glass rod. It is then kept in an oven
for about two hours at 110-115° in order to expel the hydrochloric
acid completely.2 The treatment with hydrochloric acid and the evapora-
tion and the drying in the oven are repeated in order to bring about
thorough decomposition of the silicates. The dry residue is then moistened
with concentrated hydrochloric acid and left to digest for some hours in
the cold. It is then taken up in hot water, the solution filtered and the

1  See   Lunge,   Technical Methods of   Chemical Analysis  (London,,  1908), Vol. I,
pp. 66i and 662.

2  Some consider that the silica is rendered completely insoluble only at 130°.

FIG. 6, to add a little meicurie chloride solution to re-tain the hydrogen